26 ADVENTURES IN RADIOISOTOPE RESEARCH 



Radioactive Phosporus 



As a neutron source we had only radon-beryllium, later radium-beryl- 

 lium mixtures, at our disposal. When Niels Bohr celebrated his fiftieth 

 birthday, his friends presented him with 600 milligrams of radium, which 

 he most kindly put at our disposal. With such modest neutron sources, 

 the only tracer of an element of physiological importance which could 

 be produced having sufficient activity was radiophosphorus. We irradi- 

 ated 10 liters of carbon disulphide from which carrier-free ^^P could be 

 easily separated. All our preparations, however, had an activity below 

 1 [xc . The first problem attacked was whether the mineral constituents 

 of the skeleton are renewed or not during life. Labelled phosphate was 

 administered to rats, and the specific activity of their plasma inorganic 

 phosphorus and skeleton apatite phosphorus compared. The comparison 

 indicated a 30 per cent renewal in the course of the first 24 hours. The 

 amount of phosphate involved in this process exceeded twenty times the 

 phosphorus content of the blood. Thus a large part of the phosphorus 

 present in the soft tissues must have been released and applied in the 

 replacement of skeleton phosphorus. This result demonstrated the 

 dynamicity of phosphorus metabohsm. These conclusions were pub- 

 lished about the same time, in 1935, as the first paper by Schoen- 

 heimer and Rittenberg appeared in which they demonstrated the 

 dynamic nature of fat depots. It was followed by a great number 

 of other most illuminating papers in which deuterium, and later heavy 

 nitrogen, was applied as a tracer. Since ^^P has a half-Kfe of fourteen 

 days only, happenings through life of a mouse cannot be followed using 

 this tracer. However, applying ^^Ca we succeded a few years ago in 

 showing that only one-third of the calcium atoms of the skeleton of the 

 mouse are replaced during life. 



The above-mentioned first application of an artificial radioactive 

 isotope as a tracer was followed by our investigation of whether and to 

 what extent the phosphatide molecules of the brain are renewed. These 

 investigations were extended to other organs and to the formation 

 of labelled phosphatides in the chick embryo following the injection 

 of 32p into the fertilized egg. We transfused labelled plasma of a rabbit 

 to a sister rabbit and followed the rate of disappearance of the 

 labelled phosphatide molecules from the circulation of the second rabbit 

 and their accumulation in various organs. The next step was the study 

 of the rate of renewal of the ATP, creatine, and similar molecules, partly 

 in collaboration with Professor Parnas in Lwow, Poland. With Arm- 

 strong and also with Krogh and Hoist, we studied ^sp incorporation in 

 dentine and enamel. In one of the early applications (1937), the penetra- 

 tion of 32p into yeast cells was traced and shown to be an almost one- 

 way process. This investigation was made possible by co-operation with 



